In vehicles such as automobiles, there has been a growth in the ratio of use of foamed molded bodies formed of thermoplastic resins in view of weight reduction. For conventional foamed molded bodies formed of resin compositions with fillers therein, the amount of talc has been increased for rigidity and the amount of a rubber component has been increased for impact resistance to achieve both rigidity and impact resistance (Patent Document 1). However, rigidity and impact resistance are properties conflicting to each other. In addition, when a foaming ratio is increased, it is difficult to control a foamed cell structure to be homogeneous, making it difficult to achieve both the rigidity and the impact resistance of foamed molded bodies.
Patent Document 2 describes a resin composition in which a thermoplastic elastomer and talc serving as an inorganic filler are blended to a polypropylene resin and a foaming agent is added thereto as Table 1 below:
TABLE 1Examples, Comparative ClaimsExamplesFormulationPolypropylene resin100100in parts by Thermoplastic  5.3 to 75.034.8 or 36.4masselastomerInorganic filler11.0 to 75.010.1 to 16.7 (talc) (1.8 or 2.7 μm)Organic peroxide  0 to 2.0   0 to 0.030Foaming agent 0.1 to 10.012.5
Patent Document 2 states that the 50% particle diameter (D50) of the talc is preferably 0.01 μm to 50 μm, in which one with 1.8 μm or 2.7 μm is used in Examples. As to the surface treatment of the talc, it states that the talc may be left untreated or subjected to treatment for increased dispersibility, and untreated talc is used in Examples. According to examination by the inventors of the present invention, fine talc with a 50% particle diameter of 3 μm or smaller is difficult to be dispersed during kneading and flocculates when it is added in a large amount, whereby such talc is not necessarily effective as foaming nuclei and causes an open cell structure, for example, making it difficult to achieve both rigidity and impact resistance.
The amount of organic peroxide disclosed in Examples is 0.030 part by mass at most, leaving room for improvement in making foamed cells homogeneous and balancing impact resistance, rigidity, and the like.
In addition, there is no specific description about rigidity and impact resistance.
Next, although there has been a growth in the ratio of use of foamed molded bodies formed of a polypropylene resin as described above, they are little used for material-colored design parts. This is partly because the scratch resistance of conventional polypropylene resin compositions is insufficient, and scratches are conspicuous. To impart scratch resistance, an example is described in which surface resistance is reduced through addition of a fatty acid amide such as erucamide or silicone as surface modifiers to a resin composition with talc therein (Patent Document 3). However, even when the fatty acid amide is added to the resin composition with surface-untreated talc therein, sufficient scratch resistance cannot be necessarily achieved. The inventors of the present invention studied on the reasons, and thought that this is because the fatty acid amide is absorbed by the surface-untreated talc in the early stage after molding and insufficiently transfers to the surface of molded bodies. Moreover, the addition of the fatty acid amide alone may cause failures such as the degradation of appearance quality and the occurrence of sticking with the lapse of time. The inventors studied on the reasons, and thought that this is because the fatty acid amide continues to transfer to the surface of molded bodies to accumulate with the lapse of time.